1. Field of the Invention
This invention relates to power supply regulation, and more particularly to a regulation circuit for providing timing gate signals to a power section of a power supply, such gate signals being disconnected in the presence of temporary interruptions of an applied ac source voltage.
2. Description of the Prior Art
The maintenance of power to a load, even in the presence of momentary interruptions, is critical in many applications. However, none may be more critical than in systems wherein the load is represented by high intensity, gaseous-discharge lamps. The reason for this is that even momentary cessation of power will cause the lamps to go out, requiring normally two minutes and longer to restrike and even longer to reach full brightness.
In addition to the maintenance of power in the presence of line voltage interruptions, it is also highly desirable to maintain a relatively stable voltage to many loads, such as lamp circuits, even if there are no line voltage interruptions. The main reason for this is to ensure against fluctuations that may shorten lamp life or otherwise cause lamp injury.
Circuits in the past have employed combinations of resistors, capacitors and even diodes to provide regulation to power supplies, but these have amounted to little more than filtering systems preventing widely varying excursions.
A circuit somewhat suitable for providing a degree of desirable regulation is disclosed in FIG. 7 of copending patent application Ser. No. 654,926, filed Feb. 2, 1976, commonly assigned now abandoned in favor of a continuing patent application, now issued as U.S. Pat. No. 4,134,044. In that circuit, a phototransistor controlled by the brightness of a light emitting diode connected across the dc output of the power supply determines the application of gate voltage to a triac. This conduction timing determines the operation of a bridge in the power supply, and hence provides regulation.
This circuit does not ensure against sudden surges opening the power circuit, as in the present circuit, which would basically ignore such surges and prevent them from effecting the operation of the power section of the power supply. More importantly, perhaps, it does not ensure the maintenance of a dc voltage output in the presence of momentary interruptions of the line source of ac power.
Another circuit similar to that disclosed herein is disclosed in copending patent application Ser. No. 808,969, filed June 22, 1977, also commonly assigned. In that circuit, there was the fundamental problem of not quickly removing regulation in the presence of ac source voltage outages and therefore, the regulation circuit attempted regulation at the very time that regulation was not possible. This circuit assures that under these conditions, the circuit operation will be dependent on dc voltage stored on large storage capacitors.
Therefore, it is a feature of this invention to provide an improved regulation circuit that provides regulation to the dc output of a power section of a power supply and prevents cessation of the dc output even in the presence of ac source voltage outages, for a substantial period of time.